The report is chillingly comprehensive. It says that Iran created computer models of nuclear explosions, conducted experiments on nuclear triggers and did advanced research on a warhead that could be delivered by a medium-range missile.

What gives the report particular credibility is its meticulous sourcing. The agency’s director, Yukiya Amano, built a case on more than a thousand pages of documents, the assistance of more than 10 agency member states and interviews with “a number of individuals who were involved in relevant activities in Iran.”

The United Nations Security Council — particularly Russia and China, which have been shielding Iran — has no more excuses. It needs to quickly impose a new round of even tougher sanctions on Iran, which is also enriching uranium five years after the Council ordered it to stop. Russia, which is still doing a lot of business with Iran, ruled out more sanctions, saying they would be seen as an “instrument for regime change.” China said it would study the report. The enrichment program is having technical problems, and sanctions are making it harder to import materials. But not hard enough.

We’re not sure any mix of sanctions and inducements can wean Tehran of its nuclear ambitions. We are sure that a military attack would be a disaster — and the current saber-rattling from Israel should make everyone nervous. A military strike would not set back Iran’s program for very long. It would rally Iranians around their illegitimate government. And it would produce a huge anti-Israeli and anti-American backlash around the world — whether or not Washington had tried to stop it.

The last round of sanctions was approved 17 months ago. Since then, Russia and China have balked at further penalties while stalling on implementing those already approved. So long as that enabling continues, Iran will keep pushing its nuclear program forward.

A version of this editorial appears in print on November 10, 2011, on page A34 of the New York edition with the headline: The Truth About Iran. Today's Paper|Subscribe